Lithium ion accumulator cells expand during operation and the “formation”. According to D. P. Wilkinson, Effects of Physical Constraints on Li cyclability, Journal of Power sources 36, 1991, pages 517 to 527, the morphology of the lithium in a lithium ion accumulator cell is porous even after just a few charging/discharging cycles if too little pressure (p<0.1 MPa) is exerted on the lithium ion accumulator cell, and therefore the latter fails after a few charging/discharging cycles. In order to achieve optimum power and a long service life for lithium ion accumulator cells, a defined pressure which acts on said lithium ion accumulator cells is therefore required.
However, conventional pretensioning concepts which can build up this pressure are inflexible, expensive and take up a very large amount of space.
JP 2008277085 A discloses a battery pack in which the individual battery cells, between which spacers are arranged, are fixed to one another by a strap which has apertures over the entire length. The purpose of this configuration is adequate ventilation in order to avoid overheating during operation.